1.Field of the Invention
The invention relates to a turbine, and more particularly to a turbine of a turbocharger with double-layer flow passage and variable cross-section.
2.Description of the Related Art
Currently, variable cross-section turbochargers have aroused more and more attention. To meet the requirements of variable cross-section, conventional turbines of turbochargers are provided with rotary nozzle vanes. As shown in FIG. 1 and FIG. 2, a turbine of a variable cross-section turbocharger 1 with rotary vanes includes a turbine housing 5, a volute diffuser channel 7, and a power turbine 9. The exhaust gas discharged by an engine during normal operation is collected through the turbine housing 5, passes through a volute gas feeding passage, and then is distributed around the power turbine 9 through the volute diffuser channel 7, thereby pushing the power turbine 9 to rotate at high speed. A compressor impeller 14 is driven to rotate to compress gas at high speed through a turbine rotor shaft 13 under the support of a floating bearing 12 in a middle shell 3. The compressed gas is collected through a compressor housing 2 and sent into the engine for combustion.
To make the supercharger work stably under high and low speed conditions, nozzle vanes 8 are arranged in the volute diffuser channel 7 of the turbine of the variable cross-section turbocharger 1 with rotary vanes. The nozzle vanes 8 are distributed on a nozzle ring supporting disk 6 around the power turbine 9, and the opening a1 thereof can be adjusted through a transmission mechanism 4, thereby changing the actual flow area of the volute diffuser channel 7 and the rotation speed of the power turbine 9. The high temperature gas in the engine can be discharged into the engine exhaust pipe through a volute gas outlet 10 after doing power in the power turbine 9.
The variable cross-section turbocharger 1 with rotary vanes can change the flow channel through changing the opening a1 among the nozzle vanes 8, with convenient control. However, the exhaust gas discharged from the engine generally has an exhaust temperature of about 600° C., which tends to be higher. The high exhaust temperature poses strict requirements on the nozzle vanes 8, the transmission mechanism 4, the nozzle ring support disk, and external control systems. Thus, the cost of this type of variable cross-section turbocharger is very high and the service life thereof is short, resulting in a limited market.